Centering or alignment devices are known, which compensate for positioning errors due to machine inaccuracy, misaligned components, vibration or tolerance. For instance, ATI Industrial Automation offers a “Remote Center Compliance” (RCC) device that uses a plurality of spring-loaded shear pads that align a part in a receiving hole. The RCC device is reliant on low lateral stiffness of the shear pads.
Another alignment device is offered by Robotic Accessories Division (RAD), which also provides a centralizing movement that is based on a series of ball bearings being driven into seats. The RAD device has limited lateral and radial allowances.
DE-STA-CO offers a variety of centering devices that have various limitations. For instance, DE-STA-CO's “Cylindrical Horizontal Compliance Device” is a horizontal compensator only. While it will allow for a radial movement, it will not return to its original radial position. The angular repeatability is only ±10°. Another DE-STA-CO device entitled “Lateral Compliance Device—Pneumatic Centering” only compensates in a lateral direction. This device allows no radial movement. Another device by DE-STA-CO entitled “Compliance Wrist” allows for both lateral and radial movement, but this device is akin to the ATI device noted above. The Compliance Wrist basically is a pair of plates connected by springs oriented at slight angles. The springs allow the plates to shift and/or rotate, and then urge the plates to return to their original position. This device offers no positive return for radial movement. Also, the limited range of movement (at most ±⅛″ lateral and ±2° radial) plagues this design. Another shortfall with this design is the amount of force required to shift the plates. Its springs must be strong enough to support a load, which therefore require substantial force to utilize its misalignment capability. Stated another way, this arrangement can require several hundred inch pounds for deflection.
The industry is in need of a compensator for a robotic arm that has a relatively large size to lateral travel ratio, exceptional radial movement allowance, essentially zero force to utilize compensation travel, and no axial compressibility to permit use in applications requiring axial force.